1. Field of the Invention
The present invention relates to anti-ErbB2 antibody variants or antigen-binding fragments thereof, nucleic acid molecules encoding them, and their uses.
2. Description of the Related Art
There has been reported that HER2 (ErbB2), which is a member of receptor tyrosin kinases such as EGFR (ErbB1), HER3 (ErbB3) and HER4 (ErbB4), locates on a cell membrane, and plays an important role in cell growth, differentiation and survival (Jaclyn et al. Clin Breast Cancer. 8:38-49 (2008)). There has been also reported that unlike the other HER family proteins, HER2 is not activated dependant on a ligand, and that approximately 20,000 of HER2 is expressed on a cell membrane of normal cells while approximately 20,000,000 of HER2 is expressed on a cell membrane of cancer cells (Shepard et al. J Clin Immunol. 11:117-127 (1991)). This HER2 overexpression induces many heterodimers between HER2 and HER1, or HER2 and HER3 as well as HER2-HER2 homodimers, thereby inducing cell proliferation and growth, resulting in acceleration in a transformation into cancer cells (Mayumi et al. Clin Cancer Res. 12:7242-7251 (2006)).
Until now, the overexpression of HER2 was detected in various cancers such as breast cancer (25-30%), ovarian cancer (15-30%), gastric cancer (23%), lung cancer (11-32%), renal cell carcinoma (30-40%), rectal cancer (17-90%), pancreatic cancer (26-45%), bladder cancer (44%), prostate cancer (12%), and head and neck cancer (29-39%) (Cancer Immunol Immunother 53:166-175 (2004); Clin Cancer Res 12:4377s-4383s (2006); Br J Cancer 91:1195-1199 (2004); Cancer 94:2584-2589 (2002); Cancer 98: 66-73 (2003); Int J Oncol 27: 681-685 (2005); Int J Pancreatol 17:15-21 (1995); Int J Cancer 87:349-359 (2000); Ann Oncol 12:S15-S19 (2001); J Pathol 204:317-325 (2004)). Furthermore, the overexpression of HER2 was observed in endometrial cancer, salivary gland tumor, colon cancer and thyroid cancer (Science 229:974 (1985); Lancet. 1:765-767 (1986); Mol Cell Biol. 6:955-958 (1986); Oncogene Res. 3:21-31 (1988); Oncogene 4:81-88 (1989); Cancer Res. 51:1034 (1991); Gynecol. Oncol, 38:364 (1990); Cancer Res. 50:421-425 (1990); Cancer Res. 50:5184 (1990); Cancer Res. 49:6605 (1989); Mol. Carcinog. 3:254-257 (1990); Br, J. Cancer 57:358-363 (1988); Pathobiology 59:46-52 (1991); Cancer 65:88-92 (1990)).
Herceptin (Trastuzumab, 4D5) which is an sole anticancer drug targeting HER2 received marketing approval in 1998 for the treatment of patients with metastatic breast cancer or early breast cancer whose tumors overexpress the HER2 protein, and is administered to the patient in combination with the other anticancer drugs (J. Clin. Oncol. 17:2639-2264 (1999)). Herceptin inhibits survival and proliferation of cancer cells by inhibiting the formation of HER2-HER2 homodimer (Ann Oncol 18:977-984 (2007)).
However, although Herceptin was succeeded in HER2-targeting anticancer drug, it merely exhibited response effect of 12-34% when administered solely and response effect of 38-50% when coadministered. In addition, where Herceptin was administered to patients solely or in combination with the other drugs, abnormal heart diseases were developed in 2-7% or 11-28% of the patients, and one woman among ten women could not receive the administration of Herceptin due to the risk of developing heart diseases (N Engl J Med 357:39-51 (2007)). Hence, there is a strong demand for an antibody whose side effects are less than Herceptin, and thus Omnitarg (Genetech) is undergoing phase III clinical trial (Clin Cancer Res 12:4436s-4440s (2006)). However, Omnitarg has a problem with lower efficacy as compared with Herceptin. Accordingly, it is required to develop a novel anti-HER2 antibody or improved form of which, for example 4D5 variants having improved affinity, efficacy or the like.
Generally, it is difficult to prepare an antibody with high affinity for antigen since an exposed surface of the antigen is limited. Especially, when the in vitro selection is performed from a naïve phage display library, this phenomenon more occurs. Accordingly, the affinity of antibodies prepared from the naïve phage display library is mere 10-100 nM (Iwai et al. Protein Eng Des Set. 23:185-193 (2010)).
Strategies for enhancing the affinity of antibodies are divided into a random approach and a targeted approach (Sheedy et al. Biotechnol Adv. 5(4):333-52 (2007)). The targeted approach is concerned with a strategy to introduce some mutations into specific amino acids, e.g., CDR or FR, in which targeted PCR, CDR walking, site-directed mutagenesis and CDR target hotspot are used. The random approach is concerned with a strategy to introduce some modifications into variable domains, in which error-prone PCR, DNA shuffling and chain shuffling (Kim et al. Adv Drug Deliv Rev. 58:657-667 (2006)). Various variants prepared by the above-mentioned methods are constructed as libraries, followed by displaying the various variant libraries on phage surface, and then improved variants are selected. Besides, yeast display and ribosome display are also used for the display (Rader et al. Curr Opin Biotechnol. 8:503-508 (1997); Zahnd et al. J Biol Chem. 279(18):18870-18877 (2004)).
Throughout this application, various patents and publications are referenced and citations are provided in parentheses. The disclosure of these patents and publications in their entities are hereby incorporated by references into this application in order to more fully describe this invention and the state of the art to which this invention pertains.